Reel for winding a cutting cord for a grass-cutting device and head for grass-cutting device incorporating said reel

ABSTRACT

A reel ( 1 ) for winding a cutting cord for a grass-cutting device is described, said reel comprising a first and a second series of axially and angularly staggered teeth and, having constrained with it, an axially movable slider ( 21 ) provided with a toothing ( 23 ) cooperating with the first and the second series of teeth.

TECHNICAL FIELD

The present invention relates to a reel for winding a cutting cord for agrass-cutting device in general. The invention also relates to a headfor a grass-cutting device of the type comprising a reel onto which thecutting cord is wound.

In the present description and the accompanying claims, “grass-cuttingdevice” is understood as referring to any device suitable for cuttingvegetation.

STATE OF THE ART

In the sector of machinery and devices for cutting vegetation, forexample grass, shrubs or the like, cord-cutting heads, i.e. those inwhich a cutting cord or several cutting cords wound onto a reel projectwith their ends from a rotating head, are frequently used. The portionor portions of cord projecting from the rotating head cut thevegetation, being tensioned by the centrifugal force.

The cutting cord is subject to wear and therefore numerous devices havebeen designed in order to allow lengthening of the portions of cuttingcord projecting from the head in order to restore the length thereoffollowing wear. Some of these devices are provided with a slider slidinginside a seat formed in the head and projecting from said head. Thisslider has a toothing which cooperates with a double series of teeth onthe reel. Each travel movement of the slider produces lengthening of thecutting cord by a predetermined amount. A resilient member biases theslider into the position projecting with respect to the head. In othercases the slider is seated inside a cowl covering the head and is actedon by a member operated remotely, for example by means of a pull cable,the operating end of which is associated with the handlebar of themachine on which the grass-cutting head is mounted. A device of thistype is described, for example, in EP-B-0 467 006.

In these devices removal of the reel from the head involves disassemblyof numerous parts. Reassembly of these parts is complex and requirestime as well as a certain manual dexterity. Production of the device isrelatively costly owing to the large number of parts which form it.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the present invention is to provide a reel for a cuttingcord to be used in a grass-cutting head, which overcomes the drawbacksof the conventional art.

Another object of the invention is to provide a grass-cutting head whichavoids the limitations, costs and complexities of the conventionaldevices.

These and further objects and advantages, which will be obvious topersons skilled in the art from reading of the text which follows, areobtained essentially by means of a reel which comprises a first and asecond series of axially and angularly staggered teeth and with whichthe slider is directly constrained, which slider is axially movable andprovided with a toothing cooperating with the first and the secondseries of teeth of the reel.

In this way, the slider and the reel form an assembly which may beeasily inserted into the head and removed therefrom. As will emergeclearly from the following description of some examples of embodiment, asimple, compact and economical design, which is easy-to-use andlow-cost, is obtained.

In practice, the first and the second series of teeth on the reel may beformed inside an axial hole provided in said reel, the slider beingseated in said axial hole. In order to prevent the slider from comingout of the reel and to define a maximum projecting position thereof, asuitable retaining system, for example in the form of a retaining edge,may be provided. Instead of a retaining edge, lugs projecting radiallytoward the inside of the axial hole of the reel may be provided. Theretaining edge or other system may cooperate with the toothing of theslider so as prevent it from coming out of the axial hole of the reel.

During use, when the head in which the reel is seated rotates, the reelmust be angularly coupled with the head, except during the cordlengthening operations. For this purpose, a torsional coupling surfaceis provided. The latter may be formed on the reel, but is preferablyformed on the slider since, by so doing, a broader coupling surface andtherefore a reduction in the stress on said coupling surface isachieved. Said surface may have any configuration and may be formed, forexample, as a prism-shaped surface inside the slider. Alternatively, theslider may have on its external surface grooves cooperating with lugsformed in the head into which the reel is inserted. Equivalentconfigurations are also possible, provided that they are characterizedby the presence of a torsional coupling surface, i.e. a surface whichtorsionally constrains the slider with the head inside which the reel isinserted. The latter is able to rotate with respect to the head and withrespect to the slider when the toothing of the slider is disengaged fromone of the two series of teeth so as to engage with the other series ofteeth of the reel to allow lengthening of the cutting cord.

When inserted into the reel, the slider is resiliently biased into amaximum projecting position with respect to the reel, where its toothingcooperates with one of the two series of teeth provided in said reel.For this purpose a resilient member is used. The latter may be insertedinto the axial hole of the reel and be retained between the slider and asurface of the head. However, according to a particularly advantageousembodiment, the resilient member is preferably stably seated inside thereel so that the latter may be inserted into the head and removed fromthe latter without the need for assembly and disassembly of theresilient member every time, said member remaining inside the reel.

For this purpose, according to a particularly advantageous embodiment ofthe invention, the end of the axial hole opposite to that from which theslider projects is provided with a stop for retaining the resilientmember, which thus remains compressed between the retaining stop and theslider. In this case, the reel is formed as two parts joined together.Joining may be stable and irreversible, for example by means of bonding,welding or another system.

However, according to a preferred embodiment of the invention, joiningis reversible and therefore the two joined portions may be separatedfrom each other so as to allow extraction of the resilient member. Thisis particular advantageous for recycling purposes. In fact, whereas theslider and the reel are made of plastic material, the resilient memberis normally a helical spring made of metal wire. The spring is thereforepreferably separated from the plastic material so as to allow easyrecycling of the materials.

The retaining stop provided at the end of the axial hole opposite tothat from which the slider projects may also be provided solely toprevent the slider from coming out of this end, while the resilientmember has dimensions such as not to be retained inside the reel. Inthis case, it will be compressed between the slider and a part of thehead inside which the reel is inserted.

When the reel is formed as two portions which can be joined together ina reversible manner, joining is preferably performed in the axialdirection, it being envisaged that the reel is divided into twoportions, each of which comprises a flange and an intermediatecylindrical wall. The two cylindrical walls are inserted one inside theother and form the central body of the reel inside which the axial holeis formed. The cutting cord or cutting cords are wound around thecentral wall so as to form the coils of cord which are retained betweenthe two flanges of the two portions axially joined together.

Joining may be performed by means of resilient tongues which are formedon one of the two portions into which the reel is divided, which tonguesare inserted into notches, holes or eyelets formed in the other of saidtwo portions.

Further advantageous embodiments of the reel according to the inventionare indicated in the accompanying claims which are described withreference to a few examples of embodiment.

The invention also relates to a cord-type grass-cutting head comprisinga seat with through-holes for the cutting cord and, in said seat, a reelonto which the cutting cord is wound, characterized in that the reel isconstructed in the manner described above.

Further characteristic advantages of the head according to the inventionare indicated in the accompanying claims and will be described ingreater detail with reference to the examples of embodiment illustratedin the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with reference to thedescription and the attached drawing which shows a practical nonlimitingembodiment of said invention. In the drawing:

FIG. 1 shows an exploded and split perspective view of a reel accordingto a first embodiment;

FIG. 2 shows again a split perspective view of the reel in FIG. 1 in theassembled condition;

FIGS. 3 and 4 show, similar to FIGS. 1 and 2, a different embodiment ofthe reel according to the invention;

FIGS. 5 and 6 show a perspective view of a reel from above and frombelow in the assembled condition;

FIGS. 7 and 8 show, similar to FIGS. 1 and 2, a third embodiment of thereel;

FIGS. 9 and 10 show, similar to FIGS. 7 and 8, a variation of the reel;

FIGS. 11 to 17 show, in longitudinal cross sections, heads using reelsaccording to the preceding figures in various assembled conditions.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A first embodiment of the reel according to the invention is shown inFIGS. 1 and 2, where the reel is cut in half so as to show, sectioned,the internal components thereof. The reel, which is generally denoted by1, comprises two portions 1A and 1B which are shown in the conditionseparated from one another in FIG. 1 and assembled together in FIG. 2.The portions 1A and 1B are joined together in the axial direction.

The portion 1A has a disk-shaped flange 3 and a cylindrical wall 5coaxial with the flange 3. Similarly, the portion 1B has a flange 7 anda cylindrical wall 9. In the assembled condition, the cylindrical wall 9is located inside the cylindrical wall 5, as shown in the split view inFIG. 2.

The two cylindrical walls 5 and 9 define the central body of the reelwhich is provided with an axial hole. The flange 3 has an upper opening11 coaxial with the central body of the reel, while the flange 7 of theportion 1B has an opening 13.

The opening 11 is defined by a stop formed by an internal annular flange11A. The latter is equipped, on the side directed toward the inside ofthe reel, with an annular projection 11B, for the purposes indicatedbelow. The opening 13 is delimited in turn by an annular edge 13A.

As can be seen in particular in the exploded view in FIG. 1, a firstseries of teeth 15 formed on the inner surface of the cylindrical wall 5is associated with the upper portion 1A of the reel. Similarly, teeth 17of a second series of teeth are formed on the inner surface of thecylindrical wall 9. The teeth 15 and 17 are angularly staggered when thepositions 1A and 1B are joined together. They are also axially staggeredin the sense that the teeth 15 of the first series extend axially towardthe lower portion 1B of the reel 1 over an axial length such as not toextend substantially beyond the point at which the teeth 17 of thesecond series start.

In the assembled condition, the teeth 15 of the portion 1A of the reelproject inside the cylindrical wall 9 via axial slits 9A formed in saidwall.

A slider 21 is seated inside the axial hole formed in the reel 1 anddelimited by the cylindrical walls 5 and 9. Said slider has a toothing23 along its upper edge. In the assembled condition, this toothing 23rests on the annular edge 13A which forms an edge for retaining theslider, which is thus retained inside the reel. The slider 21 has asubstantially cylindrical external surface 21A inside which andcoaxially with which an internally hollow body 25 with a cylindricalexternal surface 25A and an internal surface 25B with a hexagonal crosssection extends. A diaphragm 27 provided centrally with a hole at 27A islocated in a middle position along the axial extension of the body 25.

A seat 29 with an annular cross section for seating a resilient memberconsisting of a helical compression spring 31 is thus defined betweenthe external wall of the slider 21 and the body 25. Said spring ishoused inside the axial hole of the reel and compressed between theflange 11A of the upper portion 1A of the reel and the bottom of theslider 21, as can be clearly seen in FIG. 2. The annular projection 11Bformed on the flange 11A retains, in cooperation with the seat 29, theresilient member 31 in the correct position.

In the assembled condition, therefore, the slider 21 is able to slideinside the axial hole of the reel when it is pushed in the direction ofthe arrow F (FIG. 2), compressing the resilient member 31. In this way,the toothing 23 of the slider 21 is displaced from a position where itis located at the same height as the series of teeth 17 into a positionwhere it is located aligned with the series of teeth 15.

When the reel is inserted into a head and a cutting cord is woundthereon, the alternating movement of the slider 21 allows lengthening ofthe cutting cord owing to the centrifugal force of the head which isrotating, as will be explained in greater detail with reference to FIGS.11 to 17.

FIGS. 3 and 4 show a reel which is similar to that in FIGS. 1 and 2 andwhich differs from the latter with regard to the form of the inner partof the slider 21. The same numbers denote parts which are the same as orcorrespond to those of the reel in FIGS. 1 and 2. In FIG. 3, the body 25which is located inside the slider 21 does not have the diaphragm 27,but solely an internal cavity with a hexagonal cross section which isclosed at the bottom by the end wall of said slider 21.

Assembly of the two portions 1A and 1B of the reel 1 and of the slider21 with the respective resilient member 31 is performed in a mannersimilar to that already described.

The portions 1A and 1B of the reel may be joined together in anirreversible manner, for example by means of bonding, welding(advantageously ultrasound welding) or in any other suitable manner.According to a preferred embodiment, however, joining is performed usingreversible means which allow separation of the two portions 1A and 1B,as illustrated in FIGS. 5 and 6. These Figures show a perspective viewfrom above and a perspective view from below of a reel similar to thatin FIGS. 3 and 4, but with illustration of some accessory parts whichmay be present both on the reel in FIGS. 3 and 4 and on the reel inFIGS. 1 and 2. The same numbers denote parts which are the same as orcorrespond to those in FIGS. 1, 2, 3 and 4.

In addition to a chamfer provided along the edge of the flange 3, thereel in FIGS. 5 and 6 has—in addition to that shown in the precedingfigures—a system for securing the cord which is to be wound onto thereel. This system is denoted by 33 and consists, in this example, ofthrough-slits formed in the flange 3 of the portion 1A. A pin 35 extendstransversely with respect to the slits 33 (see FIG. 6). The cord issecured to the reel by passing it into the two openings left free by thetransverse pin 35 inside the slit 33. Systems of this type and otherequivalent systems are known per se and any securing system maybeadvantageously used on the reel according to the invention.

FIGS. 5 and 6 also show means for engaging the free ends of the cordwound onto the reel in order to facilitate insertion of the reel intothe head of the grass-cutting device. These engaging means are providedin this example in the form of radial incisions 37 formed in the flange7 of the portion 1B. The terminal ends of the cutting cord are insertedand retained inside the incisions 37 in a manner known per se.

FIGS. 5 and 6 also show a possible embodiment of means for reversibleconnection of the portions 1A and 1B forming the reel 1. Theseconnection means consist of resilient tongues 39 formed in thecylindrical wall 5 of the portion 1A of the reel 1. The tongues 39terminate in teeth 39A which engage in notches 41 formed in the flange 7of the portion 1B of the reel 1. The notches 41 are open on the side ofthe flange 7 opposite to the side directed toward the flange 3, allowingin this manner access to the terminal teeth 39A of the tongues 39 andtherefore the mutual disengagement of the two portions 1A and 1B.

FIGS. 5 and 6 illustrate, moreover, the possibility of forming on theexternal surface of the slider 21 axial grooves 21B, for the purposeswhich will be clarified below with reference to FIGS. 11 to 17.

FIGS. 7 and 8 show a variation of embodiment of the reel according tothe invention. The same numbers denote the same or corresponding parts.The reel in FIGS. 7 and 8 differs from the reel in the preceding figuresin that the portion 1A has a protuberance 50 in the form of a cap. Theprotuberance 50 has an axial hole 51 defined by a cylindrical wall 55having a bottom 57 with a through-hole 59 coaxial with the hole 51. Thecylindrical wall 55, together with the wall of the cap 50, defines aseat for retaining the resilient member 31 which performs the functionof the annular projection 11B in FIGS. 1 to 4.

The slider 21 has, in this example of embodiment, a central body 25 withan axial hole, the side surface 25B of which has a hexagonal crosssection. The axial hole defined by the hexagonal wall 25B is athrough-hole and has a constant cross section over its whole extension.

In FIGS. 7 and 8, the portions 1A and 1B are shown in the invertedcondition, in the sense that the portion 1A indicated above as upperportion is now located in the lower position. This corresponds to adifferent assembly of the reel in the cutting head, as will be clarifiedwith reference to FIGS. 11 to 17.

FIGS. 9 and 10 show a reel which is similar to that shown in FIGS. 7 and8 and which differs from the latter exclusively owing to the differentform of the cap-shaped protuberance 50 which projects at the bottom fromthe portion 1A of the reel 1. In this case, in fact, the protuberance 50has inside it a bottom wall 50A and is not provided with an axial hole.An annular projection (not shown) for laterally containing the resilientmember 31 may be provided if necessary.

FIG. 11 shows a first method of mounting the reel according to theinvention in a head of a grass-cutting device. The head of thegrass-cutting device is generally denoted by 60 and in this embodimentcomprises a seat defined by a cap-like member 63 with a bottom opening65. Radial bushes 67 are inserted in the side wall of the cap 63 and,through them, the free ends of one or more cutting cords which areschematically indicated by F1 are inserted and wound onto the reel 1.

A hub 69 of the machine on which the head 60 is mounted passes throughthe upper wall 63A of the cap 63. The hub 69 has a hexagonal prismaticouter surface which is coupled with the surface 25B of the body 25formed inside the slider 21. The hexagonal surfaces 25B of the body 25of the slider 21 and of the hub 69 form a torsional coupling whichallows the rotational movement of the hub 69 to be transmitted to theslider 21 and from the latter, via the toothing 23 and the series ofteeth 17, to the reel 1. Said hexagonal surface of the hub 69 forms atorsional coupling with the hole with a hexagonal cross section formedin the upper wall 63A of the cap 63, so as to cause rotation of saidcap.

Axial retention of the reel, and consequently of the head 60, isachieved in this example of embodiment by means of a screw 71 whichpasses through the hole 27A in the diaphragm 27 of the slider 21 andengages in a threaded hole of the hub 69.

During operation of the head, the portions of cord F1 projecting fromthe bushes 67 break and are subject to wear, with the consequent needfor restoration thereof. For this purpose, the slider 21 is pressed inthe direction of the arrow F so that the toothing 23 of the slider 21 isdisengaged from the teeth 17, assuming an axial position correspondingto that of the teeth 15 of the reel. Consequently, the reel rotatesowing to the tractional effect due to the centrifugal force of the cordsF1 through an angle corresponding to the angular phase-displacementbetween the teeth 17 and the teeth 15. The reverse movement of theslider 21 produces disengagement of the toothing 23 from the teeth 15and restoration of the position shown in FIG. 11, with the consequentfurther rotation of the reel by a further amount corresponding to theangular phase-displacement of the teeth 15 and 17. A lengthening of thecutting cord is thus obtained with each movement of the slider 21 in thetwo directions.

In the embodiment in FIG. 12, the same reel 1 is mounted in a head,again denoted by 60, similar to the head in FIG. 11, but equipped with abottom cover 66. The reel differs from that in FIG. 11 owing to thedifferent configuration of the slider 21. The reel in FIG. 11 has theform illustrated in FIGS. 1 and 2, whereas the reel in FIG. 12 has theform illustrated in FIGS. 3 and 4. The bottom cover 66 of the head 60engages along the edge of the side wall of the cap 63 by means ofresilient tongues 68 which engage in slits 66A of the cover 66 or inanother manner. The screw 71 for locking the slider and therefore thereel in the head 60 is therefore not necessary. Torsional couplingbetween the hub 69 and the reel is again achieved by means of thehexagonal surface of the hub 69 and the hexagonal surface 25B of thebody 25 formed inside the slider 21. The hub 69 has in this example ofembodiment a threaded pin 69A which engages inside a threaded hole inthe power drive of the strimmer, lawn mower or other type ofgrass-cutting device with which the head 60 is coupled. Torsionalcoupling between the head 60 and the power drive may be obtained bymeans of fastening achieved with the threaded pin 69A or in anothersuitable manner.

FIG. 13 shows the assembly consisting of the head 60 and of the samereel as FIG. 12 (shown in detail in FIGS. 3 and 4). The head in FIG. 13differs from the head in FIG. 12 in that the bottom cover 66 is notprovided. In this case, axial retention of the reel 1 inside the head isachieved by means of an internal annular rim 63B provided along thebottom opening of the cap 63 forming the head 60. Torsional coupling ofthe reel and of the head with the hub 69 may be achieved using one ofthe systems described above.

FIGS. 14, 15 and 16 show different methods of assembly of a reel of thetype illustrated in FIGS. 7 to 10 in various types of head.

More particularly, FIG. 14 shows a head similar to that in FIG. 11. Thereel 1 is mounted in this case so that the portion 1A thereof isdirected downward such that the protuberance 50 projects beyond thebottom opening 65 of the head 60. The slider 21 rests on the innersurface of the upper wall 63A of the cap 63 forming the head 60. Thelengthening movement of the cutting cord is obtained in this case bypressing the protuberance 50 on the ground during rotation of the head.This causes a raising and subsequent lowering movement of the entirereel with respect to the slider 21 (due to the effect of the resilientmember 31), the slider in this case remaining axially fixed with respectto the head 60.

Axial locking of the reel 1 is performed by means of the screw 61 whichin this case passes through the hole 51 in the protuberance 50 andthrough the hole 59 in the bottom wall 57.

FIG. 15 shows the assembly of a reel of the type illustrated in FIGS. 9and 10 on a head similar to the head in FIG. 13. Axial retention of thereel 1 in the head is also performed in this case by means of the edge63B surrounding the bottom opening of the side wall of the cap 63forming the head 60.

FIG. 16 shows the assembly of the reel in FIGS. 9 and 10 on a head ofthe type corresponding to that shown in FIG. 12. Axial retention of thereel 1 is performed by means of the bottom cover 66.

FIG. 17, finally, shows a system for assembling a reel 1 in whichtorsional coupling between the reel and the head is performed in theregion of the slider 21. The latter has (as shown in FIGS. 5 and 6 anddescribed above) longitudinal grooves 21B. Toothings 66B formed in thecover 66 of the head 60, which moreover has a form equivalent to that inFIG. 12, engage in said grooves. In this way, the rotary movement istransmitted from the hub 69 to the slider 21 and from the latter via thetoothing 23 to the reel 1 and via the grooves 21B and the toothings 66Bto the head 60.

It must be made clear that FIGS. 11 to 17 show only some of many methodsof using a reel according to the invention. The latter may in fact beused in heads of various types which are coupled in different ways withthe power drive of the machine on which they are mounted. The methodsfor coupling and transmission of the power depend, among other things,on the type of machine (with an internal combustion engine or with anelectric motor), on the dimensions of the head, on the resistancecharacteristics, etc.

It is understood that the drawing shows only an example provided by wayof practical demonstration of the invention, it being possible to varythe forms and arrangements of said invention without however departingfrom the scope of the idea underlying said invention. The presence ofany reference numbers in the accompanying claims has the purpose offacilitating reading of the claims with reference to the description andthe drawing and does not limit the scope of protection represented bythe claims

1. A reel for winding a cutting cord for a grass-cutting device,comprising a first and a second series of axially and angularlystaggered teeth, characterized in that an axially movable sliderprovided with a toothing cooperating with said first and said secondseries of teeth is constrained with said reel, said reel defining anaxial hole inside which said first and said second series of teeth arearranged and in which said slider is seated, an edge for retaining theslider, so as to prevent the slider from coming out of said axial holeof the reel, is provided at one end of said axial bole, from which saidslider projects.
 2. The reel according to claim 1, characterized in thatsaid retaining edge cooperates with said toothing of the slider so as toprevent the slider from coming out of the axial hole of the reel.
 3. Thereel according to claim 1, characterized by a torsional coupling surfacefor torsionally constraining said reel with the head inside which it isinserted.
 4. The reel according to claim 3, characterized in that saidtorsional coupling surface is formed in said slider.
 5. The reelaccording to claim 1, characterized in that said slider has, associatedwith it, a resilient member which acts on said slider in order to biasresiliently said slider.
 6. The reel according to claim 5, characterizedin that said resilient member is seated in said axial hole.
 7. The reelaccording to claim 6, characterized in that a retaining stop forpreventing said slider from coming out is provided at another end ofsaid axial hole, said resilient member is retained in said reel by saidretaining stop, the resilient member being compressed between saidretaining stop and said slider.
 8. The reel according to claim 7,characterized in that said retaining stop is formed by an annular flangewhich projects radially toward the axis of the reel and along which anannular projection directed toward the inside of the hole of the reeland coaxial therewith is provided, said resilient member being a helicalcompression spring, said annular projection retaining laterally saidhelical spring.
 9. The reel according to claim 5, characterized in thatsaid resilient member is a helical compression spring.
 10. The reelaccording to claim 1, characterized in that a retaining stop forpreventing said slider from coming out is provided at another end ofsaid axial hole.
 11. The reel according to claim 1, characterized inthat it is formed as two portions which are axially joined together. 12.The reel according to claim 11, characterized in that said two portionsare joined together in a releasable manner.
 13. The reel according toclaim 12, characterized in that said two portions are joined together bymeans of resilient tongues engaging in corresponding notches.
 14. Thereel according claim 13, characterized in that a first of said twoportions comprises a first flange and a first cylindrical wall coaxialwith said first flange, the second of said two portions comprises asecond flange and a second cylindrical wall coaxial with said secondflange, said resilient tongues are fanned in said second cylindricalwall and in that said notches are formed in the first flange.
 15. Thereel according to claim 1, characterized by an axial protuberanceopposite to said slider.
 16. A cord-type grass-cutting head, comprisinga seat with through-holes for a cutting cord and, in said seat, at leastone reel onto which said cutting cord is wound, characterized in thatsaid reel is a reel according to claim
 1. 17. A reel for winding acutting cord for a grass-cutting device, comprising a first and a secondseries of axially and angularly staggered teeth, characterized in thatan axially movable slider provided with a toothing cooperating with saidfirst and said second series of teeth is constrained with said reel,said reel being formed as two portions which are axially joinedtogether, a first of said two portions including a first flange and afirst cylindrical wall coaxial with said first flange, the second ofsaid two portions including a second flange and a second cylindricalwall coaxial with said second flange, the first cylindrical wall havinga diameter smaller than the second cylindrical wall and being insertedinside the latter, the second cylindrical wall forming a central body ofthe reel around which said cutting cord is wound so as to form a woundarrangement of cord between said two flanges.
 18. The reel according toclaim 17, characterized in that the first series of teeth is integralwith said first cylindrical wall and said second series of teeth isintegral with said second cylindrical wall, the first cylindrical wallhaving longitudinal openings for allowing the second series of teeth topass through, said openings being angularly staggered with respect tothe teeth of the first series of teeth.
 19. A cord-type grass-cuttinghead, comprising a seat with through-holes for a cutting cord and, insaid seat, at least one reel onto which said cutting cord is wound andcomprising a first and a second series of axially and angularlystaggered teeth, characterized in that an axially movable slider with atoothing cooperating with said first and said second series of teeth isconstrained with said reel, said reel and said slider being shaped toform an assembly that can be simultaneously inserted into said seat andremoved therefrom: said the reel including an axial hole inside whichsaid first and said second series of teeth are arranged and in whichsaid slider is seated.
 20. The head according to claim 19, characterizedin that said reel has a torsional coupling surface for torsionallyconstraining said reel with said head.
 21. The head according to claim20, characterized in that said torsional coupling surface is formed insaid slider.
 22. The head according to claim 19, characterized in thatsaid reel is inserted in said head so that the slider projects from theseat of the head.
 23. The head according to claim 19, characterized inthat said reel has a protuberance projecting from the opposite side tothe slider and in that it is mounted in said seat so that saidprotuberance projects from said seat.
 24. The head according to claim19, characterized in that a resilient member which acts on said sliderin order to bias resiliently said slider into a position of maximumprojection from the reel is associated with said slider.
 25. The headaccording to claim 24, characterized in that said resilient member isseated in said axial hole of the reel and retained inside it by theslider and by a retaining stop integral with said reel.
 26. The headaccording to claim 19, characterized in that said reel is formed as twoportions which are axially joined together.
 27. The head according toclaim 26, characterized in that said two portions forming the reel arejoined together in a removable manner.
 28. The head according to claim27, characterized in that said two portions of the reel are joinedtogether by means of resilient tongues engaging in correspondingnotches.
 29. The head according to claim 19, characterized in that saidslider has a retaining edge, said reel has, at the opposite end of theaxial hole with respect to the retaining edge of the slider, a retainingstop for preventing the slider from coming out.
 30. A cord-typegrass-cutting head, comprising a seat with through-holes for a cuttingcord and, in said seat, at least one reel onto which said cutting cordis wound and comprising a first and a second series of axially andangularly staggered teeth, characterized in that an axially movableslider with a toothing cooperating with said first and said secondseries of teeth is constrained with said reel, said reel defining anaxial hole inside which said first and said second series of teeth arearranged and in which said slider is seated, an edge for retaining theslider is provided at one end of said axial hole in the reel.
 31. A reelfor winding a cutting cord torn grass-cutting device, comprising a firstand a second series of axially and angularly staggered teeth,characterized in that an axially movable slider provided wit a toothingcooperating with said first and said second series of teeth isconstrained with said reel, said reel and said slider being shaped toform an assembly that can be simultaneously inserted into the grasscutting device and removed therefrom.
 32. A cutting device comprising: areel defining a hole; a first and a second series of axially andangularly staggered teeth arranged inside said hole of said reel; aslider axially movable in said hole, said slider including a toothingcooperating with said first and second series of teeth; a retainingsystem on said reel and said slider for constraining said slider to saidreel.
 33. A device in accordance with claim 32, wherein: said retainingsystem directly connects said slider to said reel.